The physiological function and mode of regulation of transglutaminases are being studied as to their role in the formation of "provisional stroma" (fibrin of fibrin-connective tissue), during tissue or bone fracture repair, and in the modulation of specific cellular processes. The coagulant seal formed at injury sites is one of the vital elements of hemostasis and diathesis. The major constituent of this coagulant gel is fibrin. Fibrin stability appears to dictate overall healing and restoration processes and ins modulated by factor XIIIa-catalyzed cross-linking of fibrin subunits (alpha chain-polymer and gamma- gamma chain dimer) and of alpha 2 antiplasmin to alpha chains of fibrin. A number of substances, such as oxygen metabolites, sulfhydryls, triglycerides (lipophilic agents), and albumin in the plasma and tissue fluids can affect the catalytic activity of factor XIIIa and other transglutaminases. Fibrin clots provide matrices for the initial phase of cell migration and anchorage, and have been found to be covalently cross-linked to cell membrane (i.e., in B16 melanoma cells). Proteases, known to be generated during hemostasis, induce activation of membrane-bound forms of transglutaminase.